This invention relates to electronics assemblies, for example to computer systems, and to thermal management thereof.
Certain systems may be employed as servers, for example in local area networks (LANS), or in wide area networks (WANs), telecommunications systems or other operations such as database management or as internet servers. Such servers may be used in so-called xe2x80x9chorizontally scaledxe2x80x9d applications in which tens or hundreds of corresponding servers are employed as part of a distributed system.
A typical computer employed for such purposes will comprise one or more processors mounted on a circuit board, together with other components such as power supply units (PSUs), hard disc drives (HDDS), fans, digital video disc (DVD) players, memory modules, ethernet ports etc. The servers may be designed in modular form so that they can be stacked together with other corresponding servers in large racks. For example, many low end servers may be designed with a modular height of one or more 44.5 mm (1xc2xe inch) high units.
It can often be a problem to ensure that such systems are cooled adequately in view of the relatively large number of electronics components in an enclosed environment. The assembly enclosure may be provided with one or more enclosure fans in one of the assembly walls which provide a flow of air through the assembly. In addition, various components such as microprocessors and the like that generate large quantities of heat may require their own fans. In such a case, microprocessors are conventionally provided with so-called xe2x80x9cimpingementxe2x80x9d fans that are placed on, and attached to, the component, or on a heat-sink that is attached to the component. The fan will therefore be mounted only a few millimetres away from the component and will blow air from the enclosure down directly onto the component or onto the heat-sink.
However, as microprocessors have become more powerful, and therefore generate larger quantities of heat, it has been difficult to ensure adequate cooling of the microprocessor, even with the use of an impingement fan. In addition, the servers may not always be employed in data centres with air conditioned environments, and ambient temperatures may therefore be relatively high. For example, the Network Equipment-Building Standard (NEBS), which forms the requirement laid down by Telcordia Technologies (formerly Bellcore), requires that such a system will operate at ambient temperatures of up to about 55xc2x0 C. without the junction temperature of the components exceeding about 85xc2x0 C.
According to one aspect of the present invention, there is provided an electronics assembly which comprises:
(i) an enclosure;
(ii) a heat-generating component located within the enclosure;
(iii)a duct that extends from the region of an aperture in a wall of the enclosure to the component; and
(iv) a fan that is located within the duct to cause a flow of air from outside the enclosure directly to the heat-generating component.
This form of assembly has the advantage that the efficiency of thermal management of the enclosure can be significantly improved. This is partly due to the fact that air for cooling the hottest components such as microprocessors is taken directly from the exterior of the enclosure rather than from within it where the temperature can be typically 10xc2x0 C. higher than outside, and also because air is not blown directly onto the component or onto the heat-sink in a direction normal to the plane of the component, thereby causing vortices within the enclosure and consequent hot spots. Instead, air can be blown in a direction generally parallel to the surface of the component and the circuit board.
The duct may be designed so that air is caused to flow from outside the enclosure to the component with substantially no mixing thereof with air in the rest of the enclosure, at least until after the air has passed the heat-generating component, thereby ensuring that the air has not been heated up by the other components before it is used to cool the heat-generating component. There will, in general, be some degree of mixing of the air in the duct and in the remainder of the enclosure since the duct is not designed to be air tight, but, by use of the duct it is possible to reduce the mixing of air to the extent that the temperature of the air that is blown onto the component is closer to that of the ambient air outside the enclosure than to that of the air in the remainder of the enclosure.
The heat generating component may be mounted on a generally planar circuit board, for example it may be surface mounted or mounted in a dual in line I.C. package and the duct may cause the cooling air to flow in a direction generally parallel to the circuit board, in contrast with conventional impingement fans. For example, where a heat sink is provided on the component, it may be provided with cooling fins that extend outwardly from the surface of the component, and the duct may cause the air to flow between the fins and parallel to the surface of the component, so that there is relatively little disturbance to the flow of the air by the component or the heat sink, as compared with the case of an impingement fan.
According to one aspect of the invention, the duct is formed in a plurality of parts, and different parts of the duct are attached to different parts of the enclosure. For example, if the parts of the duct are joined together along the axis of the duct, and one part of the duct is attached to a lid of the enclosure, then the duct will automatically be opened when access to the duct is obtained by opening the lid, thereby facilitating access to the fan for the purposes of replacement.
According to another aspect of the invention, there is provided a method of cooling a heat-generating component in an electronics assembly, which comprises:
(i) providing a duct that extends from the region of a wall of the enclosure to the heat-generating component; and
(ii) causing air to flow along the duct from outside the enclosure to the heat-generating component.